Experimental Study of the Effect of Roughness and Broad Crested Weir Height on Discharge Coefficient

In many water supply and energy projects, such as dams, releasing of a certain flow rate and development of a structure for discharging excessive capacity over a specific time is essential. The structures which are responsible for such task are called weir structure. Such weirs possess high complexity and it is so important to analyze their hydraulic parameters, especially with the use of physical and hydraulic models. Broad crested weirs are extensive used in water transfer system as a tool for measuring the intensity of the stream and controlling water level, due to their economic-effectiveness during construction. With regard to the abundant applications of broad crested weirs, applying any modification on dimension of the sections of these weirs will make these tools more effective in terms of economic. In the present research, the optimum discharge coefficient of the flow was computed by performing experimental studies on the various models. Moreover, variation of discharge coefficient, Froude Number, Upper water level and other hydraulic parameters were simulated using a physical model of broad crested weirs fabricated in hydraulic laboratory and by applying variations on height of the weirs and installing roughness on crown surface. Totally, 75 tests were performed and the results showed that increase in weir crown surface roughness, the discharge coefficient decreases up to 10 percent. Also, the discharge rate increases up to 22 percent, with increase of weir height.